PIE base ‘to drive, draw, move’, probably related to PIE base *agro- ‘field’, root of acre, agriculture, pilgrim, and peregrine.
Derivatives include act, agony, agent, pedagogue ‘leader of children’, exact, cogitate, synagogue, antagonize, protagonist, examine, navigate, and many others.
[Pokorny *ag̑- ‘to lead’, pp. 4–6.]